Field of the Invention
This invention relates particularly to a back-fire preventive unit for a gas cutting torch for fusion-cutting of metal frames and plates by ejecting out of a cutting tip a mixed gas obtained by mixing a fuel gas and oxygen for igniting it, and thus by utilizing the flames which have been built up on the cutting tip.
In a manual gas cutting torch, a flame port is formed at its tip, a handle section for holding the torch with one hand is formed at the middle, and the connection ports with gas and oxygen cylinders are built up at the rear section, or in many cases, at the rear end of said handle, to whose connection port and handle section the adjusting valves for regulating the flowrate of gas and oxygen are fitted.
The manual gas cutting torch in this way serves to help an operator to hold it with his one hand for performing the fusion-cutting work while moving it freely. However, flash-backs sometimes happen in this type of gas cutting torch. A back-fire phenomenon occurs when the jet speed "Uf" of mixed gases and oxygen becomes smaller than the combustion speed "Sb" of the mixed gases while the relation between them usually remains at Uf=Sb. A back-fire is usually found when regulating the gas and oxygen volumes or when extinguishing the fire. The biggest reason for the back-fire to happen in such a case is that the equilibrium between the jet speed "Uf" and the combustion speed "Sb" of mixed gas is disturbed by the adjustment of gas and oxygen, and the value of "Uf" frequently becomes smaller.
Should a back-fire happen in a gas cutting torch, this back-fire runs back up to the gas or oxygen cylinder which might explode.
Therefore, in the past to avoid the possibility of explosion a fire preventive unit is attached to the outlet port of the cylinder or to the hose connecting the cylinder with the gas cutting torch. However, this type of conventional means is not satisfactory for the operator's safety although it can prevent the cylinder from exploding.
In many cases the operator holds the gas cutting torch in his one hand during work with the other effective hand, and while, adjusting the gas or oxygen, he holds the gas cutting torch with the hand opposite to his effective hand. For this reason, once a back-fire should happen, this gas cutting torch instantaneously becomes high in temperature and his one hand is burned. Also, due to this instantaneous high temperature he sometimes drops the gas cutting torch from his hand, and this is especially dangerous when dropping the gas cutting torch from a high place. Further, there may be an explosion to the handle section which incorporates a valve for adjusting the gas or oxygen. In case of this explosion, a serious injury may be invited to the operator's body in addition to the burn to his hand or a part of his body.